Technical Field
The present invention relates to optical communications and, more particularly, to transmitter pre-distortion in optical transmitters using semiconductor lasers.
Description of the Related Art
Short-reach interconnects using multi-mode optical fiber (MMF), over distances on the order of 100 m, are widely used in computer systems, data centers, and campus networks. For these data links, the optical channel contributes relatively little signal degradation for 10-40 Gb/s data rates. In addition, generations of fiber with optimized modal bandwidth continue to be developed that minimize the optical channel as the primary source of signal degradation. The biggest challenge for short-reach interconnects is to produce active components, namely optical transmitters and receivers, that provide sufficient bandwidth to operate at high data rates (e.g., >25 Gb/s) while maintaining low power consumption to maximize the power efficiency (commonly expressed in mW/Gb/s or pJ/bit: the energy required to transmit a bit of information).
One conventional approach to implementing an optical link is to separate the transmitter and receiver, designing each separately. The transmitter is optimized to make its digital optical output as ideal as possible, while the receiver is designed to receive the transmitted optical signal and convert the optical signal to an electrical signal with high sensitivity (i.e., to operate with as little optical power as possible at a given bit-rate) with minimum added jitter. Both transmitter (TX) and receiver (RX) are designed to meet specifications while consuming a minimum amount of power. The most straightforward method for building optical TXs and RXs is to use high-speed analog drivers and receiver amplifiers that have sufficient bandwidth to faithfully convert the electrical signal to an optical signal and back again with minimal distortion. However, as data rates have increased beyond 10 Gb/s, it is difficult to realize optical devices (lasers and detectors) and amplifier circuits that have sufficient raw bandwidth with acceptable power consumption. To achieve the highest data rates, the lasers are operated at high current densities and the circuits typically consume large amounts of electrical power to deliver high speed performance.